<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>flex布局-侧轴对齐方式</title>
  <style>
    .box {
      display: flex;
      /* 弹性盒子在侧轴方向没有尺寸才能拉伸 */
      /* align-items: stretch; */

      /* 垂直居中 */
      align-items: center;

      /* align-items: flex-start; */

      /* align-items: flex-end; */

      height: 300px;
      border: 1px solid #000;
    }

    /* 第二个div，侧轴居中对齐 */
    .box div:nth-child(2) {
      align-self: center;
    }

    .box div {
      width: 200px;
      height: 100px;
      background-color: pink;
    }
  </style>
</head>
<body>
  <div class="box">
    <div>1</div>
    <div>2</div>
    <div>3</div>
  </div>
</body>
</html>